Birth Order and Personality: What's the science behind sibling rank?

For ages, parents and psychologists have sworn that birth order – who came first, who is the baby of the family, and who is sandwiched in between – influences the person we become. But is there any science to back that? The truth is, from the mix of all the other things that determine who we become (think DNA, relationships, life events, and emotional ties) researchers have a hard time pinpointing that any one trait is really the result of birth order.

Still, a few birth order generalizations do hold up under the microscope. After all, scientists and psychologists have plenty of explanations for why order matters. For one, a mom’s prenatal environment is known to change (in hormones, nutrition, etc.) with each successive pregnancy. After birth, firstborns tend to get more attention and investment from parents, a hierarchy creeps in with the arrival of new brothers and sisters, kids pick certain roles or niches within the family to differentiate themselves, and, through what psychologists call de-identification, siblings sometimes actively try to be different from the ones before them.

So what does science tell us about birth order?

Firstborn

In 2007, Norwegian epidemiologists reported in Science that firstborn children tend to have a slight boost in smarts compared to their younger siblings. The study of 250,000 siblings found that firstborns had a three-point IQ advantage over their closest brother or sister. The second born was one point ahead of the third and, after that, the effect faded.

Most explain the edge by saying that firstborn children have more one-on-one parent time and the responsibility of teaching and taking care of younger siblings. A recent study estimated that firstborns get approximately 3,000 hours more time with their parents between the ages of four and 13 than the younger siblings get when they pass through the same ages. Many think the attention makes them sharp and responsible, with a greater pressure to succeed and do things properly – and then parents tend to loosen up on subsequent kids. It’s hard to back that observation up with evidence but, for example, some note that firstborns on average earn more money and achieve higher education levels. Nobel Prize winners and National Merit scholars are disproportionately made up of firstborns.

Lastborn

Popular wisdom says that the youngest – who never quite shakes the role of being the baby of the family – tends to be more free-spirited, adventurous, risky, and creative.

Youngest siblings often don’t have as many care-taking responsibilities and may have more freedom to do things their own way. Some say families have a kind of Darwinian survival of the fittest principle happening, with each new child having to elbow her way into territory that isn’t already spoken for. A lastborn who comes into a pack of already straight-and-narrow siblings might carve out her own niche by being more spunky and daring.

As with most psychological theories, you probably know some babies of the family who fit this description and others who don’t. The data here is pretty thin, but for example, UC Berkeley researchers found that younger siblings are 1.5 times more likely to take on riskier and more aggressive sports like football. And, in a study of major league baseball players, those who are younger brothers are 10 times more likely to attempt base-stealing and have better batting success than firstborn baseball players. If you can read into sports behavior, that means lastborns are the daredevils of the family.

Middle child

Alfred Adler, a contemporary of Freud and one of the first psychologists to propose the relevance of birth order, started the popular conception that middle children – squeezed between the oldest and the baby – tend to be agreeable team players who know how to deal well with others.

Middle kids theoretically don’t get any stretch of time living alone with mom and dad. Whether this is a good or bad thing is a matter of opinion. Middle kids could get lost in the mix and feel left out of special roles and privileges, or end up being especially emotionally savvy, because they’re always challenged to stay dialed in and navigate the goings-on of the people around them. And some research does suggest that younger siblings (not necessarily the middles, but anyone who comes after the firstborn) have greater “theory of mind” skills – the ability to see things from other people’s perspectives.

How much does birth order effect your kids?

Some parents will read these descriptions and see their kids exactly. Others will dismiss any notion that these dynamics exist in their own families. And to that end, it’s important to note that no matter what science tells us, birth order can hardly seal our children’s fate. Our little ones’ personalities are still a random mix of our own genetic quirks, the chemical blend in which they were bathed in the womb, and the different experiences they create and bump into during childhood. If birth order really does nudge them in certain directions, it’s only one small piece of an elaborate puzzle.

What do you think? Do any of the first, middle, or lastborn leanings apply to the family you came from, or to your kids?

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